It might be a rather late reply, but for the record of anyone that searches the forums on this topic, I'll try to explain:

The "now playing" plugin for some media players, like Windows Media Player and Winamp and such are really quite simple. Any application can send a simple command to MSN to change that message.
How the command is implemented can differ. I think the problem is that your plugin only updates the text in MSN when a new song starts. Normally that'd work fine because it doesn't need to change the title displayed in MSN halfway a track. However, since SST is a stream, technically your media players will treat it as one long track that lasts as long as you want to play it. The metadata (=title, artist, etc) of the stream is updated every now and then but it never starts a new track in the playlist of Windows Media Player.
Since it never starts a new track, the plugin never updates the message in MSN. It might update it at the start, but before it got any metadata there is no title to show.

How to fix this problem? If you want this to work, you'll have to find a plugin for your media player that can deal with variable metadata. This can be hard to find and I'm not sure it even exists. Many media players like Winamp have a forum where you can post requests for plugins like this, and perhaps you can request a fix for variable metadata as well on the site you got the plugins from. You could also try to find other media players to see if there exists a plugin that works for those.